Traditionally, the materials that have been used in photocatalysis have been metal containing, where the metal includes one or more transition metals including copper, platinum, indium, gallium, arsenic etc. and suffer drawbacks such as metal instability in different oxidation states, cost, toxicity and difficulty associated with the manufacture of these materials. Recent work in Germany and China by Antonetti and co-workers [1] shows that metal-free polycarbon nitride can be used in photocatalytic reaction mentioned above due to the favorable band gap associated with optical absorption, a value which is about 2.7 eV and is strategically placed in an energy scale that is efficient in degradation of organic molecules under visible light. However, the efficiency with which the degradation takes place is low and not practical due to the very low amount of light absorbed above 420 nm. Since most of the visible spectrum lies above that value (up to 800 nm) the quantum yield and efficiency of the catalytic process is very low.
It would be desirable to shift the onset of visible light absorption to higher values so that more of the visible light is absorbed which may translate to a more efficient photocatalysis for organic molecule degradation as well as photocatalytic splitting of water. Besides the band gap the positions of the valence band and the conduction band is important. The band gap required for splitting water is greater than 1.23 eV (less than 1000 nm). However in case of visible light a band gap of less than 3.0 eV (greater than 400 nm) is required. The band gap should be preferably between 2.43 eV and 3.3 eV. Both the reduction and oxidation potential of water should lie within the band gap of the photocatalytic material. The energy of the valence band has to be lower than the oxidation potential of oxygen in order to generate oxygen, while the energy of the conduction band has to be higher than the reduction potential of hydrogen. When light interacts with the surface of the photocatalyst charge separation into excited photons and holes are created which correspond to conduction and valence bands respectively. Recombination of these must be avoided for higher efficiency devices and practical applications. Electron mobility to the surface may be desirable to keep the charges separated.
To achieve the above stated desired properties researchers have incorporated graphite or graphene in the mixture by preparing carbon nitride in the presence of graphite sheets. The procedure involved the preparation of a melamine-graphite immiscible mix which was then heated to a temperature of 550° C. in the presence of nitrogen gas till the melamine molecules condensed to carbon nitride. The product was shown to be a layered structure comprising of carbon nitride and graphene. The composite was shown to be superior than graphitic carbon nitride (i.e., carbon nitride that exists in a 2D form similar to graphite). Thus the composite made of alternating layers of pristine graphitic carbon nitride and pristine graphite exhibited better photocatalytic degradation properties than pristine graphitic carbon nitride alone.
However, the use of pre-made graphite in the above-mentioned process adds more time, cost and complexity because it adds to the steps required preparing the material. Furthermore, the preparation using premade graphite yields a composite consisting of carbon nitride and graphite/graphene that are not covalently linked to each other, which is not desirable.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.